DC-to-DC converters are power converters that convert one direct current (DC) voltage into another DC voltage. If the converter converts an input voltage from a higher voltage to a lower output voltage, it is known as a buck converter. A typical buck converter connects the first terminal of the inductor to an input voltage and uses a pair of switches that alternatively connect the second terminal of the inductor to an output terminal or to ground to regulate the output voltage at the second terminal of the inductor to the desired level. If the converter converts an input voltage from a lower voltage to a higher output voltage, it is known as a boost converter. A typical boost converter uses a pair of switches that alternatively connect a first terminal of an inductor to an input voltage or to ground to regulate the output voltage at the second terminal of the inductor to a desired level. If the converter converts a variable input voltage that may be slightly higher or slightly lower than the desired output voltage, it is known as a buck-boost converter because it is capable of alternatively operating in the buck more, in boost mode, or in the buck-boost mode based on the relationship between the input voltage and the desired output voltage. Buck-boost converters typically use four switches connected to an inductor that are alternatively conductive to control the mode of operation. Buck-boost converters have become increasingly popular in recent years due to the large number of consumer products that operate using batteries whose voltage varies over a wide range.
DC-DC power converters typically operate using pulse width modulation (PWM) based on a reference clock signal. In general PWM converters have poor efficiency during light load conditions that are common in battery-powered products. In order to overcome these limitations, PWM converters often add a second control loop to improve efficiency during light load conditions in which the second loop uses skip mode, pulse frequency modulation, frequency foldback, or hysteretic conversion. However dual loop systems suffer from poor load transients when switching between normal and light loads.
The use of the same reference symbols in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.